1. Field of the Invention
The invention relates to crosslinkable substances based on organosilicon compounds, to the preparation thereof and to the use thereof.
2. Background Art
Addition-crosslinking substances crosslink by attachment of Si-bonded hydrogen to an aliphatic carbon-carbon multiple bond (hydrosilylation) in the presence of a catalyst, typically a platinum compound. After mixing the components, a ready-for-use, crosslinkable composition is obtained, however, such compositions frequently exhibit only a limited pot life, since the crosslinking reaction is already underway. This makes it necessary to use the composition soon after its preparation. There have therefore been many attempts to prevent premature initiation of the crosslinking reaction, which normally proceeds even at ambient temperature, using “inhibitors”. Reference may be had for example, to U.S. Pat. No. 3,445,420, which discloses the use of vinyl-rich siloxanes or α-hydroxyacetylenes as inhibitors. These inhibitors inhibit both hydrogen elimination by condensation, and crosslinking via hydrosilylation.
Phosphorus(III) compounds, such as phosphites or trialkylphosphines, are generally very powerful inhibitors which normally so strongly inhibit platinum that the crosslinking and hydrogen evolution process either fails completely, or the composition does not completely crosslink and remains tacky. In the patent literature, the use of P(III) compounds has already been known for a long time. Trialkyl- or triarylphosphines have been proposed as inhibitors, alone or in the form of, e.g., tetrakisphosphineplatinum complexes and also in mixtures with platinum/vinyl complexes (e.g., U.S. Pat. No. 4,851,452) as catalyst/inhibitor system; similar attempted solutions have been pursued for the preparation of rapidly foaming silicone compositions with particularly low density. Reference may be made for this, for example, to U.S. Pat. No. 4,851,452 and U.S. Pat. No. 4,840,974. U.S. Pat. No. 4,329,275 discloses systems based on phosphorus(III) which oxidize a phosphite to give the corresponding phosphate, by the addition of peroxide under the action of heat, which phosphate then for lack of free electron pairs can no longer act as a sigma donor and consequently no longer acts as an inhibitor. This naturally results in the restriction to thermally curing systems which quickly vulcanize, and during the course of which, again exhibit kinetics of hydrogen formation and crosslinking which closely overlap. Trialkyl or triaryl phosphites are used with other thermally curing systems. Reference may had, for example, to EP-A 0 761 759 and WO 98/29497, which disclose the possibility of crosslinking due to mono- or polydentate phosphite ligands to be initiated only by the influence of heat.